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7 Definitions of Usability Usability represents a balance between the TASK, the USER, and the SYSTEM to achieve a particular PURPOSE within an environment. Users can achieve their goals in an effective, efficient, and satisfactory way. Easy-to-use, early-to-learn, user friendly, easy-to- implement, and user accessible.

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8 Why do we design unusable products? 1. Common-sense design is good enough. 2. The more functionality the better! 3. We can evaluate the interface later.... 4. Weve always done it this way. 5. My boss said I had to design it this way. 6. Users can customize their interfaces any way they want. 7. Im a user!

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10 HFE Focus Design out the potential for human error Design in ease-of-learning and ease-of-use

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11 Benefits of Human Factors Evidence shows that product usability is the market differentiator of the future. ( Harvard Business Review, July-August 1991, A Rappaport & S Halevi ) If you do not do usability testing on your product, then the customer will do it for you Reduced Development Cost Increased Sales Increased Product Quality Increased Customer Satisfaction Reduced Service and Maintenance Costs Reduced Documentation Reduced Liability

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25 What Is a Usability Study What Is a Usability Study A subjective and objective evaluation of how well a system meets the needs of its users. System – a combination of the product, the environment, and the user Needs – expectations, knowledge, skills, abilities, performance, norms… Users – purchasers, managers, end users, maintainers… Usability is an iterative process

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26 What Is a Usability Study What Is a Usability Study Types of usability studies Inquiry – used to obtain information about users likes/ dislikes, needs, system understanding via observation, interview, and survey Field observation, Focus groups, Interviews and Questionnaires Testing – used to identify where interface could better support user by having users work on typical tasks with the product Performance measurement, Thinking aloud, Teaching method Inspection – used to identify deviation from established guidelines or standards through expert review Heuristic evaluations, Cognitive and Pluralistic walk- throughs, Feature and label inspections

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27 How Do You Prepare a Study How Do You Prepare a Study Map Usability Concerns to Participants Determine sample size Within-subjects requires fewer participants than between- subjects Usability focused on finding gross problems, statistical power less important, small frequent samples OK * Nielsen and Landauer, 1993. A mathematical model of the finding of usability problems. Proc. ACM INTERCHI 93 Conference, Amsterdam, the Netherlands, 24-29 April Usually 5-8 participants »4 participants will find 70% of major usability issues »8 participants will find 85%, diminishing returns above 8* Use a larger sample if investigating a specific interface issue